Farnesoid X Receptor Knockout Mice Research Articles

Farnesoid X Receptor: Effective alleviation of rifampicin -induced liver injury

Antituberculosis drugs induce pharmacologic cholestatic liver injury with long-term administration. Liver injury resulting from rifampicin is potentially related to the bile acid nuclear receptor Farnesoid X Receptor (FXR). To investigate this, cholestasis was induced in both wild-type (C57BL/6N) mice and FXR knockout (FXR-null) mice through administration of rifampicin (200 mg/kg) via gavage for 7 consecutive days. Compared with C57BL/6N mice, FXR-null mice exhibited more severe liver injury after rifampicin administration, characterized by enlarged liver size, elevated transaminases, and increased inflammation. Moreover, under rifampicin treatment, FXR knockout impairs lipid secretion and exacerbates hepatic steatosis. Significantly, the expression of metabolism molecules BSEP increased, while NTCP and CYP7A1 decreased following rifampicin administration in C57BL/6N mice, whereas these changes were absent in FXR knockout mice. Furthermore, rifampicin treatment in both C57BL/6N and FXR-null mice was associated with elevated c-Jun N-terminal kinase phosphorylation (p-JNK) levels, with a more pronounced elevation in FXR-null mice. Our study suggests that rifampicin-induced liver injury, steatosis, and cholestasis are associated with FXR dysfunction and altered bile acid metabolism, and that the JNK signaling pathway is partially implicated in this injury. Based on these results, we propose that FXR might be a novel therapeutic target for addressing drug-induced liver injury.

FXR deletion attenuates intestinal barrier dysfunction in murine acute intestinal inflammation.

Accumulating literature suggests that the farnesoid-X receptor (FXR), a nuclear bile acid receptor best known for its role in bile acid homeostasis, is also a potent context-dependent regulator of inflammation. FXR may thus be relevant to several intestinal disease states including inflammatory bowel disease, necrotizing enterocolitis, and sepsis. In this study, we tested the effects of FXR deletion on acute murine intestinal inflammation. We found that FXR knockout (KO) mice were protected from intestinal injury and barrier dysfunction induced by lipopolysaccharide (LPS) injection, dithizone (DI)/Klebsiella, and cecal ligation/puncture models. In the LPS model, RNA sequencing and qPCR analysis showed that this protection correlated with substantial reduction in LPS-induced proinflammatory gene expression, including lower tissue levels of Il1a, Il1b, and Tnf. Examining functional effects on the epithelium, we found that LPS-induced tight junctional disruption as assessed by internalization of ZO-1 and occludin was ameliorated in FXR KO animals. Taken together, these data suggest a role for FXR in the intestinal barrier during inflammatory injury.NEW & NOTEWORTHY Intestinal barrier failure is a hallmark in gut-origin sepsis. We demonstrate that the intestinal barriers of farnesoid-X receptor (FXR) knockout (KO) animals are protected from inflammatory insult using multiple models of acute intestinal inflammation. This protection is due to decreased inflammatory cytokine production and maintenance of tight junctional architecture seen within the KO animals. This is the first report of FXR deletion being protective to the intestinal barrier.

Loss of the DNA-binding domain of the farnesoid X receptor gene causes severe liver and kidney injuries

Farnesoid X receptor (FXR) regulates bile acid synthesis, lipid metabolism, and glucose homeostasis in metabolic organs. FXR-knockout (FXR-KO) mice lacking the last exon of the FXR gene develop normally and display no prenatal and early postnatal lethality, whereas human patients with mutations in the DNA-binding domain of the FXR gene develop severe hepatic dysfunction. In this study, we generated novel FXR-KO mice lacking the DNA-binding domain of the FXR gene using CRISPR–Cas9 technology and evaluated their phenotypes. Similar to the aforementioned FXR-KO mice, our novel mice showed elevated serum levels of total bile acids and total cholesterol. However, they were obviously short-lived, showing severe liver and renal pathologies at an early age. These results indicate that FXR, including its unknown isoforms, has more significant functions in multiple organs than previously reported. Thus, the novel FXR-KO mice could lead to a new aspect that requires reworking of previous knowledge of FXR in the liver and renal function.

Puerarin Modulates Hepatic Farnesoid X Receptor and Gut Microbiota in High-Fat Diet-Induced Obese Mice.

Obesity is associated with alterations in lipid metabolism and gut microbiota dysbiosis. This study investigated the effects of puerarin, a bioactive isoflavone, on lipid metabolism disorders and gut microbiota in high-fat diet (HFD)-induced obese mice. Supplementation with puerarin reduced plasma alanine aminotransferase, liver triglyceride, liver free fatty acid (FFA), and improved gut microbiota dysbiosis in obese mice. Puerarin's beneficial metabolic effects were attenuated when farnesoid X receptor (FXR) was antagonized, suggesting FXR-mediated mechanisms. In hepatocytes, puerarin ameliorated high FFA-induced sterol regulatory element-binding protein (SREBP) 1 signaling, inflammation, and mitochondrial dysfunction in an FXR-dependent manner. In obese mice, puerarin reduced liver damage, regulated hepatic lipogenesis, decreased inflammation, improved mitochondrial function, and modulated mitophagy and ubiquitin-proteasome pathways, but was less effective in FXR knockout mice. Puerarin upregulated hepatic expression of FXR, bile salt export pump (BSEP), and downregulated cytochrome P450 7A1 (CYP7A1) and sodium taurocholate transporter (NTCP), indicating modulation of bile acid synthesis and transport. Puerarin also restored gut microbial diversity, the Firmicutes/Bacteroidetes ratio, and the abundance of Clostridium celatum and Akkermansia muciniphila. This study demonstrates that puerarin effectively ameliorates metabolic disturbances and gut microbiota dysbiosis in obese mice, predominantly through FXR-dependent pathways. These findings underscore puerarin's potential as a therapeutic agent for managing obesity and enhancing gut health, highlighting its dual role in improving metabolic functions and modulating microbial communities.

Aspirin Caused Intestinal Damage through FXR and ET-1 Signaling Pathways.

Aspirin is a non-steroidal, anti-inflammatory drug often used long term. However, long-term or large doses will cause gastrointestinal adverse reactions. To explore the mechanism of intestinal damage, we used non-targeted metabolomics; farnesoid X receptor (FXR) knockout mice, which were compared with wild-type mice; FXR agonists obeticholic acid (OCA) and chenodeoxycholic acid (CDCA); and endothelin-producing inhibitor estradiol to explore the mechanisms of acute and chronic intestinal injuries induced by aspirin from the perspective of molecular biology. Changes were found in the bile acids taurocholate acid (TCA) and tauro-β-muricholic acid (T-β-MCA) in the duodenum, and we detected a significant inhibition of FXR target genes. After additional administration of the FXR agonists OCA and CDCA, duodenal villus damage and inflammation were effectively improved. The results in the FXR knockout mice and wild-type mice showed that the overexpression of endothelin 1 (ET-1) was independent of FXR regulation after aspirin exposure, whereas CDCA was able to restore the activation of ET-1, which was induced by aspirin in wild-type mice in an FXR-dependent manner. The inhibition of ET-1 production could also effectively protect against small bowel damage. Therefore, the study revealed the key roles of the FXR and ET-1 pathways in acute and chronic aspirin-induced intestinal injuries, as well as strategies on alleviating aspirin-induced gastrointestinal injury by activating FXR and inhibiting ET-1 overexpression.

Sex Dimorphic Effects of Bile Acid Metabolism in Liver Cancer in Mice

Background & AimsHepatocellular carcinoma (HCC) is a male-dominant disease, but targeted sex hormone therapies have not been successful. Bile acids are a potential liver carcinogen and are biomolecules with hormone-like effects. A few studies highlight their potential sex dimorphism in physiology and disease. We hypothesized that bile acids could be a potential molecular signature that explains sex disparity in HCC. Approach & ResultsWe employed the farnesoid X receptor knockout (FxrKO) mouse model to study bile acid-dependent HCC. Temporal tracking of circulating bile acids determined over 80% of FxrKO females developed spontaneous cholemia (i.e., serum total bile acids ≥40 μM) as early as 8 weeks old. Opposingly, FxrKO males were highly resistant to cholemia with ∼23% incidence even when 26 weeks old. Yet, FxrKO males demonstrated higher levels of deoxycholate than females. Compared to males, FxrKO females had more severe cholestatic liver injury and further aberrancies in bile acid metabolism. Yet, FxrKO females expressed more detoxification transcripts and had greater renal excretion of bile acids. Intervention with CYP7A1 (rate limiting enzyme for bile acid biosynthesis) deficiency or taurine supplementation either completely or partially normalized bile acid levels and liver injury in FxrKO females. Despite higher cholemia prevalence in FxrKO females, their tumor burden was less compared to FxrKO males. An exception to this sex-dimorphic pattern was found in a subset of male and female FxrKO mice born with congenital cholemia due to portosystemic shunt, where both sexes had comparable robust HCC. ConclusionsOur study highlights bile acids as sex-dimorphic metabolites in HCC except in the case of portosystemic shunt.

FXR controls insulin content by regulating Foxa2-mediated insulin transcription

Farnesoid X receptor (FXR) is a nuclear ligand-activated receptor of bile acids that plays a role in the modulation of insulin content. However, the underlying molecular mechanisms remain unclear. Forkhead box a2 (Foxa2) is an important nuclear transcription factor in pancreatic β-cells and is involved in β-cell function. We aimed to explore the signaling mechanism downstream of FXR to regulate insulin content and underscore its association with Foxa2 and insulin gene (Ins) transcription. All experiments were conducted on FXR transgenic mice, INS-1 823/13 cells, and diabetic Goto-Kakizaki (GK) rats undergoing sham or Roux-en-Y gastric bypass (RYGB) surgery. Islets from FXR knockout mice and INS-1823/13 cells with FXR knockdown exhibited substantially lower insulin levels than that of controls. This was accompanied by decreased Foxa2 expression and Ins transcription. Conversely, FXR overexpression increased insulin content, concomitant with enhanced Foxa2 expression and Ins transcription in INS-1 823/13 cells. Moreover, FXR knockdown reduced FXR recruitment and H3K27 trimethylation in the Foxa2 promoter. Importantly, Foxa2 overexpression abrogated the adverse effects of FXR knockdown on Ins transcription and insulin content in INS-1 823/13 cells. Notably, RYGB surgery led to improved insulin content in diabetic GK rats, which was accompanied by upregulated FXR and Foxa2 expression and Ins transcription. Collectively, these data suggest that Foxa2 serves as the target gene of FXR in β-cells and mediates FXR-enhanced Ins transcription. Additionally, the upregulated FXR/Foxa2 signaling cascade could contribute to the enhanced insulin content in diabetic GK rats after RYGB.

Melatonin improves cholestatic liver disease via the gut-liver axis.

Cholestatic liver disease is characterized by disturbances in the intestinal microbiota and excessive accumulation of toxic bile acids (BA) in the liver. Melatonin (MT) can improve liver diseases. However, the underlying mechanism remains unclear. This study aimed to explore the mechanism of MT on hepatic BA synthesis, liver injury, and fibrosis in 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC)-fed and Mdr2-/- mice. MT significantly improved hepatic injury and fibrosis with a significant decrease in hepatic BA accumulation in DDC-fed and Mdr2-/- mice. MT reprogramed gut microbiota and augmented fecal bile salt hydrolase activity, which was related to increasing intestinal BA deconjugation and fecal BA excretion in both DDC-fed and Mdr2-/- mice. MT significantly activated the intestinal farnesoid X receptor (FXR)/fibroblast growth factor 15 (FGF-15) axis and subsequently inhibited hepatic BA synthesis in DDC-fed and Mdr2-/- mice. MT failed to improve DDC-induced liver fibrosis and BA synthesis in antibiotic-treated mice. Furthermore, MT provided protection against DDC-induced liver injury and fibrosis in fecal microbiota transplantation mice. MT did not decrease liver injury and fibrosis in DDC-fed intestinal epithelial cell-specific FXR knockout mice, suggesting that the intestinal FXR mediated the anti-fibrosis effect of MT. In conclusion, MT ameliorates cholestatic liver diseases by remodeling gut microbiota and activating intestinal FXR/FGF-15 axis-mediated inhibition of hepatic BA synthesis and promotion of BA excretion in mice.

Farnesoid X Receptor Agonist GW4064 Protects Lipopolysaccharide-Induced Intestinal Epithelial Barrier Function and Colorectal Tumorigenesis Signaling through the αKlotho/βKlotho/FGFs Pathways in Mice

The farnesoid X receptor (FXR)/βKlotho/fibroblast growth factors (FGFs) pathway is crucial for maintaining the intestinal barrier and preventing colorectal cancer (CRC). We used an FXR agonist, GW4064, and FXR-knockout (FXR-KO) mice to investigate the role of FXR/Klothos/FGFs pathways in lipopolysaccharide (LPS)-induced intestinal barrier dysfunction and colon carcinogenesis. The results showed that upregulation of FXR in enterocytes effectively ameliorated intestinal tight-junction markers (claudin1 and zonula occludens-1), inflammation, and bile acid levels, thereby protecting mice from intestinal barrier dysfunction and colon carcinogenesis. GW4064 treatment increased FXR, αKlotho, βKlotho, FGF19, FGF21, and FGF23 in wild-type mice exposed to LPS, while FXR-KO mice had decreased levels. FXR-KO mice exhibited elevated colon cancer markers (β-catenin, LGR5, CD44, CD34, and cyclin D1) under LPS, underscoring the pivotal role of FXR in inhibiting the development of colon tumorigenesis. The varying gut microbiota responses in FXR-KO mice versus wild-type mice post LPS exposure emphasize the pivotal role of FXR in preserving intestinal microbial health, involving Bacteroides thetaiotaomicron, Bacteroides acidifaciens, and Helicobacter hepaticus. Our study validates the effectiveness of GW4064 in alleviating LPS-induced disruptions to the intestinal barrier and colon carcinogenesis, emphasizing the importance of the FXR/αKlotho/βKlotho/FGFs pathway and the interplay between bile acids and gut microbiota.

Hepatic farnesoid X receptor is necessary to facilitate ductular reaction and expression of heme biosynthetic genes.

Bile, which contains bile acids, the natural ligands for farnesoid x receptor (FXR), moves from the liver to the intestine through bile ducts. Ductular reaction often occurs during biliary obstruction. A subset of patients with erythropoietic protoporphyria, an inherited genetic mutation in heme biosynthetic enzyme ferrochelatase, accumulate porphyrin-containing bile plugs, leading to cholestasis. Here, we examined the link between FXR, bile plug formation, and how heme biosynthesis relates to this connection. We treated female and male wild-type and global and tissue-specific Fxr knockout mice with a diet containing 3,5-diethoxycarbonyl-1,4-dihydrocollidine, an inhibitor of ferrochelatase, and examined the expression of heme biosynthetic genes. We mined FXR mouse ChIP-Seq data, performed biochemical and histological analysis, and tested HepG2 and primary human hepatocytes after treatment with obeticholic acid, an FXR agonist. We observed that hepatic but not intestinal Fxr loss resulted in reduced bile plugs and ductular reaction in the liver. Then, we examined if FXR plays a regulatory role in heme biosynthesis and found significantly lower porphyrin accumulation in 3,5-diethoxycarbonyl-1, 4-dihydrocollidine-fed Fxr knockout mice. Gene expression and FXR mouse ChIP-Seq atlas analysis revealed that FXR orchestrates the expression of multiple heme biosynthetic enzymes. Finally, human HepG2 cells and primary human hepatocytes treated with obeticholic acid, showed increased expression of several heme biosynthetic genes. Overall, our data show that hepatic Fxr is necessary to maintain ductular reaction and accumulation of bile plugs. FXR can direct the expression of multiple heme biosynthetic genes. Thus, modulating FXR activity in EPP patients may help alleviate its associated liver disease.

The Role of the Nuclear Receptor FXR in Arsenic-Induced Glucose Intolerance in Mice.

Inorganic arsenic in drinking water is prioritized as a top environmental contaminant by the World Health Organization, with over 230 million people potentially being exposed. Arsenic toxicity has been well documented and is associated with a plethora of human diseases, including diabetes, as established in numerous animal and epidemiological studies. Our previous study revealed that arsenic exposure leads to the inhibition of nuclear receptors, including LXR/RXR. To this end, FXR is a nuclear receptor central to glucose and lipid metabolism. However, limited studies are available for understanding arsenic exposure-FXR interactions. Herein, we report that FXR knockout mice developed more profound glucose intolerance than wild-type mice upon arsenic exposure, supporting the regulatory role of FXR in arsenic-induced glucose intolerance. We further exposed mice to arsenic and tested if GW4064, a FXR agonist, could improve glucose intolerance and dysregulation of hepatic proteins and serum metabolites. Our data showed arsenic-induced glucose intolerance was remarkably diminished by GW4064, accompanied by a significant ratio of alleviation of dysregulation in hepatic proteins (83%) and annotated serum metabolites (58%). In particular, hepatic proteins "rescued" from arsenic toxicity by GW4064 featured members of glucose and lipid utilization. For instance, the expression of PCK1, a candidate gene for diabetes and obesity that facilitates gluconeogenesis, was repressed under arsenic exposure in the liver, but revived with the GW4064 supplement. Together, our comprehensive dataset indicates FXR plays a key role and may serve as a potential therapeutic for arsenic-induced metabolic disorders.

Loss of Farnesoid X receptor (FXR) accelerates dysregulated glucose and renal injury in db/db mice.

End-stage renal disease is primarily caused by diabetic kidney disease (DKD). The Farnesoid X receptor (FXR), a member of the nuclear receptor superfamily, has anti-inflammatory, lipid-lowering and hypoglycemic properties. It also inhibits renal fibrosis. Although its physiological role is not fully understood, it also plays a role in the control of diabetic nephropathy (DN). In the present study, we examined male FXR & leptin receptor double knockout mice, in which weight, blood glucose, body fat, and other indicators were monitored. After 6 months of rearing, blood and urine samples were collected and biochemical parameters were measured. Fibrosis was assessed by Masson's stain, while the assessment of the resuscitation case's condition was performed using succinate dehydrogenase (SDHA) stain immunohistochemistry, which measures aerobic respiration. Expression of molecules such as connective tissue growth factor (CTGF), SMAD family members 3 (Smad3) and 7 (Smad7), and small heterodimer partner were detected by RT-PCR and Western blotting as part of the application. FXR knockout decreased body weight and body fat in db/db mice, but increased blood glucose, urine output, and renal fibrosis. Primary mesangial cells (P-MCs) from FXR+/+ mice stimulated with transforming growth factor β1 (TGFβ1) showed significantly higher levels of related fibrosis factors, TGFβ1 and Smad3 mRNA and protein, and significantly reduced levels of Smad7. These effects were reversed by the action of FXR agonist chenodeoxycholic acid (CDCA). P-MCs from FXR-/- mice stimulated with TGFβ1 resulted in an increase in the expression and protein levels of collagen I and TGFβ1, and the addition of CDCA had no significant effect on TGFβ1 stimulation. However, compared with FXR+/+db/db mice, the rate of oxygen consumption, the rate of carbon dioxide production, and the rate of energy conversion were increased in FXR-/-db/db mice, whereas the SDHA succinate dehydrogenase, a marker enzyme for aerobic respiration, was significantly decreased. These results provide evidence that FXR plays a critical role in the regulation of mesangial cells in DN. The likely mechanism is that aberrant FXR expression activates TGFβ1, which induces extracellular matrix accumulation through the classical Smad signaling pathway, leading to mitochondrial dysfunction.

Celastrol as an intestinal FXR inhibitor triggers tripolide-induced intestinal bleeding: Underlying mechanism of gastrointestinal injury induced by Tripterygium wilfordii

BackgroundTripterygium wilfordii has been widely used for the treatment of rheumatoid arthritis, which is frequently accompanied by severe gastrointestinal damage. The molecular mechanism underlying the gastrointestinal injury of Tripterygium wilfordii are yet to be elucidated. MethodsTransmission electron microscopy, and pathological and biochemical analyses were applied to assess intestinal bleeding. Metabolic changes in the serum and intestine were determined by metabolomics. In vivo (time-dependent effect and dose-response) and in vitro (double luciferase reporter gene system, DRATs, molecular docking, HepG2 cells and small intestinal organoids) studies were used to identify the inhibitory role of celastrol on intestinal farnesoid X receptor (FXR) signaling. Fxr-knockout mice and FXR inhibitors and agonists were used to evaluate the role of FXR in the intestinal bleeding induced by Tripterygium wilfordii. ResultsCo-treatment with triptolide + celastrol (from Tripterygium wilfordii) induced intestinal bleeding in mice. Metabolomic analysis indicated that celastrol suppressed intestinal FXR signaling, and further molecular studies revealed that celastrol was a novel intestinal FXR antagonist. In Fxr-knockout mice or the wild-type mice pre-treated with pharmacological inhibitors of FXR, triptolide alone could activate the duodenal JNK pathway and induce intestinal bleeding, which recapitulated the pathogenic features obtained by co-treatment with triptolide and celastrol. Lastly, intestinal bleeding induced by co-treatment with triptolide and celastrol could be effectively attenuated by the FXR or gut-restricted FXR agonist through downregulation of the duodenal JNK pathway. ConclusionsThe synergistic effect between triptolide and celastrol contributed to the gastrointestinal injury induced by Tripterygium wilfordii via dysregulation of the FXR-JNK axis, suggesting that celastrol should be included in the quality standards system for evaluation of Tripterygium wilfordii preparations. Determining the mechanism of the FXR-JNK axis in intestinal bleeding could aid in the identification of additional therapeutic targets for the treatment of gastrointestinal hemorrhage diseases. This study also provides a new standard for the quality assessment of Tripterygium wilfordii used in the treatment of gastrointestinal disorders.

Farnesoid X receptor protects against lipopolysaccharide-induced endometritis by inhibiting ferroptosis and inflammatory response

Endometritis is an inflammatory condition that affects the endometrium; it is induced by bacterial infection and often leads to infertility and repeated abortions. FarnesoidXreceptor (FXR) is a member of the nuclear receptor superfamily that mediates a variety of inflammatory diseases. In the present study, we determined the protective effects of FXR on lipopolysaccharide (LPS)-induced endometritis in mice and the underlying mechanisms. The results showed that LPS administration reduced the expression of FXR in the uterus, and treatment with the FXR agonist GW4064 and fexaramine significantly alleviated the endometritis induced by LPS. In addition, compared with wild-type (WT) mice, FXR-knockout mice had more severe inflammatory responses in their uteri after LPS treatment. Moreover, ferroptosis was increased during LPS-induced endometritis, as shown by increased levels of malondialdehyde (MDA) and iron, and decreased levels of superoxide dismutase (SOD), glutathione (GSH), GXP4 and SLC7A11. In addition, inhibition of ferroptosis by treatment with ferrostation-1 (Fer-1) and liproxstatin (Lip-1) alleviated LPS-induced endometritis. Additionally, FXR-knockout mice were used to determine the relationship between FXR and ferroptosis. The results showed that knockout of FXR induced ferroptosis, and an FXR agonist inhibited LPS-induced ferroptosis. Finally, the regulatory effects of obeticholic acid (OCA) on FXR/ferroptosis and endometritis were assessed. The results showed that treatment with OCA increased the expression of FXR, decreased the levels of ferroptosis, and inhibited the endometritis induced by LPS. In conclusion, the results showed that activation of FXR can alleviate LPS-induced endometritis by inhibiting ferroptosis, and FXR may be a potential therapeutic target for treating endometritis.

Early Deregulation of Cholangiocyte NR0B2 During Primary Sclerosing Cholangitis.

Primary sclerosing cholangitis (PSC) is a probable autoimmune liver disease characterized by persistent and progressive biliary inflammation that leads to biliary infection, cirrhosis, or cholangiocarcinoma. Genome-wide omics data are scarce regarding this severe disease. MEDLINE database gene prioritization by text mining (biliary inflammation, biliary fibrosis, biliary stasis) was integrated in distinct omics data: (1) PSC liver transcriptome training and validation cohorts, (2) farnesoid X receptor (FXR) mice liver transcriptome subjected to an FXR agonist or FXR knockout mice; (3) liver single-cell transcriptome of the Abcb4-/- mice model of PSC. A liver molecular network highlighted the involvement of nuclear receptor subfamily 0 group B member 2 (NR0B2) and its associated nuclear receptor FXR in a metabolic cascade that may influence the immune response. NR0B2 upregulation in PSC liver was independent of gender, age, body mass index, liver fibrosis, and PSC complications. Heterogeneity of NR0B2 upregulation was found in cholangiocyte cell types in which the NR0B2-based cell fate decision revealed the involvement of several metabolic pathways for detoxification (sulfur, glutathione derivative, and monocarboxylic acid metabolisms). Genes potentially implicated in carcinogenesis were also discovered on this cholangiocyte trajectory: GSTA3, inhibitor of DNA binding 2, and above all, TMEM45A, a transmembrane molecule from the Golgi apparatus considered as oncogenic in several cancers. By revisiting PSC through PubMed data mining, we evidenced the early cholangiocyte deregulation of NR0B2, highlighting a metabolic and premalignant reprogramming of the cholangiocyte cell type. The therapeutic targeting of NR0B2 could potentiate that of FXR and enable action on early events of the disease and prevent its progression.

Psyllium Fiber Protects Against Colitis Via Activation of Bile Acid Sensor Farnesoid X Receptor

Fiber-rich foods promote health, but mechanisms by which they do so remain poorly defined. Screening fiber types, in mice, revealed psyllium had unique ability to ameliorate 2 chronic inflammatory states, namely, metabolic syndrome and colitis. We sought to determine the mechanism of action of the latter. Mice were fed grain-based chow, which is naturally rich in fiber or compositionally defined diets enriched with semi-purified fibers. Mice were studied basally and in models of chemical-induced and T-cell transfer colitis. Relative to all diets tested, mice consuming psyllium-enriched compositionally defined diets were markedly protected against both dextran sulfate sodium- and T-cell transfer-induced colitis, as revealed by clinical-type, histopathologic, morphologic, and immunologic parameters. Such protection associated with stark basal changes in the gut microbiome but was independent of fermentation and, moreover, maintained in mice harboring a minimal microbiota (ie, Altered Schaedler Flora). Transcriptomic analysis revealed psyllium induced expression of genes mediating bile acids (BA) secretion, suggesting that psyllium's known ability to bind BA might contribute to its ability to prevent colitis. As expected, psyllium resulted in elevated level of fecal BA, reflecting their removal from enterohepatic circulation but, in stark contrast to the BA sequestrant cholestyramine, increased serum BA levels. Moreover, the use of BA mimetics that activate the farnesoid X receptor (FXR), as well as the use of FXR-knockout mice, suggested that activation of FXR plays a central role in psyllium's protection against colitis. Psyllium protects against colitis via altering BA metabolism resulting in activation of FXR, which suppresses pro-inflammatory signaling.

RF03 | PMON288 Determining Mechanisms of Farnesoid×Receptor Regulation of Heme Biosynthesis and Ductular Reaction

Abstract Bile acids are increasingly becoming recognized as hormones, and their main endogenous receptor is the farnesoid X receptor (FXR). In order to investigate whether FXR is necessary to maintain proliferation of the bile ducts in response to injury, we challenged male and female wild-type (WT) and Fxr knockout (FxrKO) mice with 0.1% 1,4 dihydro 2,4,6 trimethyl 3,5 pyridinediacarboxylic acid diethyl ester (DDC) in the diet for two weeks. DDC is an inhibitor of ferrochelatase, the final enzyme of heme biosynthesis, resulting in a buildup of bile plugs in the liver causing an inflammatory response called ductular reaction. We found that deletion of Fxr led to a dramatic reduction in the ductular reaction independent of the sex. Then we tested if the inhibition of ferrochelatase was compensated for in FxrKO mice by analyzing the expression of genes in the heme biosynthesis pathway. Although we find a decrease in basal Alad gene expression in FxrKO mice in both sexes, upon DDC treatment, expression does not decrease as much as seen in the WT mice. Intriguingly, we also noted sex-specific changes. Cpox expression was increased in male FxrKO mice, but FxrKO mice showed reduced suppression of Cpox expression when treated with DDC. Conversely, Ppox expression was reduced in male FxrKO mice compared to WT mice, and both male WT and FxrKO mice had a comparable reduction in Ppox expression upon DDC treatment. Female FxrKO mice showed a significant decrease in Fech expression basally that did not change with DDC treatment. These results suggest that FXR may contribute towards regulating expression of genes in the heme biosynthesis pathway. However, these observations do not explain the lack of ductular reaction. Since PGC1α was previously shown to control heme biosynthesis through its downstream targets, FOXO1 and NRF1, we examined their transcript expression in our study to determine if the pathway is playing a role in our observations. We examined this pathway and observed a significant decrease in Foxo1 expression in both sexes of WT and FxrKO mice basally but only a reduction in Nrf1 expression upon DDC treatment. We are currently investigating other potential regulators of heme biosynthesis and ductular reaction, such as Klf1 which regulates erythropoiesis and plays a role in ductular reaction and the nuclear receptors Rev-Erbα/β that use heme as a ligand, to determine how FXR is regulating heme biosynthesis. Presentation: Saturday, June 11, 2022 1:24 p.m. - 1:29 p.m., Monday, June 13, 2022 12:30 p.m. - 2:30 p.m.

OR23-1 FXR Regulates the Expansion and Metabolic Function of Adipose Tissue upon Caloric Excess

Abstract Obesity is a major risk factor for developing metabolic diseases. Adipose tissue stores excess calories during obesity. Nuclear receptor Farnesoid X receptor (FXR) is expressed in various tissues and transcriptionally regulates lipid and glucose metabolism. However, the role of FXR in regulating adipose expansion is unknown. We showed that Fxr transcript is expressed in mature adipocytes isolated from both white (WAT) and brown (BAT) adipose tissues. In adipocyte-specific Fxr knockout (Ad-FxrKO) mice, we found enlarged adipocytes and decreased expression of lipolytic genes upon 60% high fat diet (HFD) or high fat/high sucrose western diet challenge. Transcriptomic analysis of WAT from Ad-FxrKO and control mice upon chow or HFD revealed that many genes involved in glucose and lipid homeostasis are misregulated in Ad-FxrKO mice with distinct patterns under normal and obese conditions. Since WAT stores fat and BAT generates heat, we examined both these depots in Ad-FxrKO mice and found reductions in the expression of mitochondrial genes and energy expenditure. Intriguingly, we found ectopic fat accumulation in the liver and systemic glucose intolerance in Ad-FxrKO compared to the control mice during obesity. Overall, these findings implicate that FXR may regulate lipid metabolism and mitochondrial functions in the adipose tissue, which consequently impacts whole-body energy homeostasis. Presentation: Monday, June 13, 2022 11:15 a.m. - 11:30 a.m.

Ginsenoside Rc attenuates DSS-induced ulcerative colitis, intestinal inflammatory, and barrier function by activating the farnesoid X receptor.

Objectives: Farnesoid X receptor (FXR) activation is involved in ameliorating inflammatory bowel disease (IBD), such as ulcerative colitis (UC), and inflammatory regulation may be involved in its mechanism. Ginsenoside Rc (Rc) is a major component of Panax ginseng, and it plays an excellent role in the anti-inflammatory processes. Our aim is to explore the alleviative effect of Rc on dextran sulfate sodium (DSS)-induced inflammation and deficiencies in barrier function based on FXR signaling. Materials and Methods: In vitro, we treated human intestinal epithelial cell lines (LS174T) with LPS to explore the anti-inflammatory effect of Rc supplementation. In vivo, a DSS-induced IBD mice model was established, and the changes in inflammatory and barrier function in colons after Rc treatment were measured using the disease activity index (DAI), hematoxylin and eosin (H&E) staining, immunofluorescence, ELISA, and qPCR. Molecular docking analysis, luciferase reporter gene assay, and qPCR were then used to analyze the binding targets of Rc. DSS-induced FXR-knockout (FXR-/-) mice were used for further validation. Results: Rc significantly recovered the abnormal levels of inflammation indexes (TNF-α, IL-6, IL-1β, and NF-KB) induced by LPS in LS174T. DSS-induced C57BL/6 mice exhibited a significantly decreased body weight and elevated DAI, as well as a decrease in colon weight and length. Increased inflammatory markers (TNF-α, IL-6, IL-1β, ICAM1, NF-KB, F4/80, and CD11b displayed an increased expression) and damaged barrier function (Claudin-1, occludin, and ZO-1 displayed a decreased expression) were observed in DSS-induced C57BL/6 mice. Nevertheless, supplementation with Rc mitigated the increased inflammatory and damaged barrier function associated with DSS. Further evaluation revealed an activation of FXR signaling in Rc-treated LS174T, with FXR, BSEP, and SHP found to be upregulated. Furthermore, molecular docking indicated that there is a clear interaction between Rc and FXR, while Rc activated transcriptional expression of FXR in luciferase reporter gene assay. However, these reversal abilities of Rc were not observed in DSS-induced FXR-/- mice. Conclusion: Our findings suggest that Rc may ameliorate inflammation and barrier function in the intestine, which in turn leads to the attenuation of DSS-induced UC, in which Rc may potentially activate FXR signaling to protect the intestines from DSS-induced injury.

Gypenosides ameliorate high-fat diet-induced non-alcoholic steatohepatitis via farnesoid X receptor activation.

BackgroundGypenosides (Gyps), the major botanical component of Gynostemma pentaphyllum, was found to up-regulate the farnesoid X receptor (FXR) in a mouse model of non-alcoholic steatohepatitis (NASH). However, the exact role of FXR and underlying mechanisms in Gyps-mediated effects on NASH remain to be elucidated.PurposeThis study investigated whether Gyps attenuates NASH through directly activating FXR in high-fat diet (HFD)-induced NASH, and delineated the molecular pathways involved.Study designA mouse model of HFD-induced NSAH was used to examine effects of Gyps on NASH with obeticholic acid (OCA) as a positive control, and the role of FXR in its mechanism of action was investigated in wild-type (WT) and FXR knockout (KO) mice.MethodsWT or FXR KO mice were randomly assigned into four groups: normal diet (ND) group as negative control, HFD group, HFD + Gyps group, or HFD + OCA group.ResultsTreatment with Gyps and OCA significantly improved liver histopathological abnormalities in HFD-induced NASH, reduced the non-alcoholic fatty liver disease (NAFLD) activity score (NAS), and lowered hepatic triglyceride (TG) content compared with the HFD group. In agreement with these liver tissue changes, biochemical tests of blood samples revealed that alanine aminotransferase (ALT), aspartate aminotransferase (AST), TG, total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), fasting blood glucose (FBG), and fasting insulin (FINS) levels were significantly lower in the HFD + Gyps vs. HFD group. Furthermore, Gyps and OCA treatment significantly up-regulated hepatic FXR, small heterodimer partner (SHP), carnitine palmitoyltransferase 1A (CPT1A), and lipoprotein lipase (LPL) expression, and significantly down-regulated sterol-regulatory element binding protein 1 (SREBP1), fatty acid synthetase (FASN), and stearoyl-CoA desaturase 1 (SCD1) protein levels compared with the HFD group in WT mice but not in FXR KO mice. Notably, Gyps- and OCA-mediated pharmacological effects were significantly abrogated by depletion of the FXR gene in FXR KO mice.ConclusionGyps ameliorated HFD-induced NASH through the direct activation of FXR and FXR-dependent signaling pathways.